Since electronic equipment is designed to be smaller, lighter, of higher performance, less expensive and of higher reliability, active passive elements constituting electronic circuits of electronic equipment are accordingly required to also be smaller.
Recently, leadless high density IC semiconductor chips to meet the above requirements have been used in electronic circuits of various electronic equipment.
In the IC semiconductor chip mentioned above, each element formed therein is directly connected to a printed circuit board through a special electrical connector, not by wire bonding or the like, using very fine metallic wires.
The electrical connector has in its housing electrical contacts which correspond to a conductive electrode pattern on an insulating carrier substrate onto which the IC semiconductor chip is mounted and carried, the contact sections of the contacts being pressed in electrical contact with the electrode pattern, and, at the same time, terminal sections of the contacts extend to the exterior of the housing so that they are connected to conductive paths of a printed circuit, etched circuit, or multilayer board or the like.
Generally, the distance between the electrodes formed on an IC semiconductor chip carrier is so small that it is difficult to connect the electrodes to a printed circuit board with sufficient isolation between each other, therefore, conversion of pitch of the contacts is essential to expand the connection pitch by spacings the contacts between the IC chip carrier and the printed circuit board.
For this purpose, two types of conventional pitch-changing contacts are presently known, such as shown in FIGS. 1A and 1B. Both are formed from lead frames 1, 11. The shapes of contacts 1b, 11b, which project perpendicularly from the carrier strips 1a, 11a of the lead frames 1, 11, are changed in such a manner that the contact portions 1c are offset from the positions of contact portions 11c by one-half of the pitch P which is respectively the pitch of the contacts 1b, 11b, the series of contacts being formed by bending each contact portion at its dotted line position. These two types of contacts are arranged in such a way that each of the contact portions 1c of FIG. 1A is centrally positioned between two adjacent contact portions 11c of FIG. 1B in the same plane, and also the contact portions 1d and 11d are sheared or cut from carrier strips 1a, 11a of lead frames 1, 11 along the line l--l so that they are positioned parallel in two rows respectively and are spaced a distance P between contact portions 1d or 11d. Thus, the spacing between contact portions 1d or 11d is twice the distance between contact portions 1c, 11c combined (1/2P). According to this arrangement, attachment of contact portions 1d, 11d to a printed circuit board (not shown) is made relatively easier by expanding the pitch of contact portion 1d or 11d by twice the pitch of contact portions 1c, 11c combined.
However, the pitch-changing contacts heretofore described and illustrated have the following disadvantages:
(1) Two types of pitch-changing contacts must be separately formed and secured to a housing by pressing-in, thermal crimping, etc., so that the height of the contact portions varies, especially due to the dimensional tolerance of insertion holes for the contacts provided on the housing, and consequently, the resulting contact pressure between the contact portions and conductive electrode pattern varies and possibly results in adverse effects on the electrical and mechanical characteristics of an electrical connector.
(2) Since two types of pitch-changing contacts are necessary, separate lead frames must be used respectively for them so that material for stamping and forming into predetermined shapes is wasteful, resulting in higher product cost.
(3) Use of two types of small pitch-changing contacts makes assembly operation inefficient and more costly.